JP3941464B2 - Manufacturing method of nitride semiconductor light emitting device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a gallium nitride-based compound semiconductor (In _X Al _Y Ga _1-XY N, 0 ≦ used in a light emitting diode (LED), a laser diode (LD), or other electronic device, power device, light receiving device, or the like. X ≦ 1, 0 ≦ Y ≦ 1, and X + Y ≦ 1) In particular , the present invention relates to an electrode, particularly an electrode (negative electrode) formed on an n-type gallium nitride compound semiconductor layer (hereinafter referred to as an n-type layer). )
[0002]
[Prior art]
In recent years, blue light-emitting diodes of practical level and blue lasers capable of continuous oscillation at room temperature have been realized. In addition, high-luminance full-color image quality using light-emitting diodes and high-density short-wave blue light-emitting elements for high-density recording on digital video disks (DVDs) using lasers or other electronic devices, power devices, light-receiving devices, etc. Further development is underway for realization. One of the developments is improving luminous efficiency.
The luminous efficiency is improved when the contact resistance between the nitride semiconductor layer and the electrode is low and the ohmic contact is good, thereby reducing the forward voltage.
The present inventors described in Japanese Patent Application Laid-Open No. 7-45867 as an electrode of an n-type layer (hereinafter referred to as n-electrode) having good ohmic contact with an n-type nitride semiconductor layer (hereinafter simply referred to as n-type layer). An n-electrode made of titanium and aluminum is disclosed. However, since the electrode described in this publication tends to oxidize aluminum, the bonding strength between the ball and n-electrode formed from a wire during bonding tends to be weakened.
[0003]
In addition, the present inventors disclosed an n-electrode made of titanium (Ti), aluminum (Al), and a metal having a higher melting point than Al in JP-A-7-221103. This technique can improve ohmic contact and electrode durability.
[Patent Document 1]
JP 7-45867 A [Patent Document 2]
JP-A-7-221103 [Patent Document 3]
Japanese Patent Laid-Open No. 03-203284 [Patent Document 4]
Japanese Patent Laid-Open No. 04-225280
[Problems to be solved by the invention]
However, although the above technique is good for an LED, an LD that has a higher current density than that of an LED and generates a large amount of heat at the electrode tends to deteriorate the electrode, and the life of the element is reduced, which is not satisfactory.
Accordingly, an object of the present invention is to provide a nitride semiconductor light emitting device having an n electrode which is formed on an n-type layer and obtains a preferable ohmic contact with the n-type layer, and which has an n electrode which is not easily altered even under severe use conditions. is there.
[0005]
That is, the object of the present invention can be achieved by the following constitutions (1) to ( 3 ).
(1) A method of manufacturing a nitride semiconductor light emitting device having at least a gallium nitride-based n-type nitride semiconductor and a gallium nitride-based p-type nitride semiconductor, the surface of the n-type nitride semiconductor having titanium, Using two or more metals from a first electrode material consisting of at least one of zirconium and tungsten and a second electrode material consisting of at least one of aluminum, silicon and germanium, and laminating each metal as a multilayer film, On top of that, a third electrode material made of rhodium, two or more metals from the first electrode material or the second electrode material are used, and the first electrode material and the second electrode material are formed as a multilayer film. Laminating and laminating the third electrode material thereon to form an electrode material;
A method of manufacturing a nitride semiconductor light emitting device, comprising: after the step of forming the electrode material, alloying a part or all of the multilayer film by annealing the electrode material.
(2) The nitride semiconductor light-emitting element according to (1), wherein, in the step of forming the electrode material, a fourth electrode material made of gold is formed on the third electrode material. Manufacturing method.
(3) In the step of forming the electrode material, the first electrode material is laminated in contact with the n-type nitride semiconductor, and the second electrode material and the third electrode material are sequentially formed thereon. The manufacturing method of the nitride semiconductor light-emitting device according to (1) or (2), wherein the layers are stacked.
[0006]
That is, according to the present invention, the combination of the above-mentioned specific metals, particularly Rh, is used as the material for the n-electrode, thereby preventing electrode deterioration due to good ohmic contact and oxidation, and improving the durability of the electrode. I made it.
Further, it is preferable to provide Au on the uppermost part of the electrode because it can satisfactorily prevent deterioration of the electrode such as oxidation, and can further improve the adhesion between the ball and the n electrode.
[0007]
[Embodiment]
The n-electrode of the present invention is composed of first to third electrode materials and a fourth electrode material in order to improve the effects of the present invention. Moreover, you may contain another metal if it is a range which does not inhibit the effect of this invention.
The first electrode material is at least one of Ti, Zr, and W, the second electrode material is at least one of Al, Si, and Ge, and the third electrode material is Rh. The first electrode material and the second electrode material composed of two or more kinds may be used alone or in combination of two or more metals.
[0008]
The n-electrode of the present invention is formed by laminating metal thin films made of a first electrode material to a third electrode material. Here, any of the electrode materials in the present invention may be formed in contact with the n-type nitride semiconductor, and the stacking order of the electrode materials is not particularly limited. Further, the same electrode material may be used twice or more at the time of electrode formation.
For example, the first electrode material is laminated in contact with the n-type layer, the second electrode material is laminated on the first electrode material, and finally the third electrode material is laminated. The order of stacking that has been performed can be mentioned. Examples of the stacking order in which the same electrode material is used twice or more include a stacking order in which the electrode materials are stacked in the first, second, first, and finally third order.
Such lamination is preferable because ohmic contact can be obtained with good reproducibility. In addition, when the third electrode material is farthest from the n-type layer in the above-described stacking order, that is, when it is stacked on the top of the n electrode, the third electrode material Rh has a higher melting point than the second electrode material. It is effective in preventing oxidation of the electrode because it is difficult to oxidize.
[0009]
Also, when two or more kinds of metals are used as the electrode material, for example, when two or more kinds of metals are used as the first electrode material, each of the metals is laminated at the time of electrode formation to form a multilayer film or two or more kinds of metals. The metal is alloyed and laminated. The first to third electrode materials may be any combination. For example, [Ti, Al, Rh], [Ti, Si, Rh], [Zr, Al, Rh], [(Ti-W), Ge, Rh], [W, (Al -Si), Rh], [Ti, Al, Ti, Rh], etc. can be combined. The combination of each of the above electrode materials is only an example, and the present invention is not limited to this. Further, the order of stacking at the time of electrode formation in the combination of the above electrode materials can be various.
In the above example, the ratio of each metal is particularly limited when the first and second electrode materials use two or more metals, for example, the first electrode material uses two metals of Ti and W. It can be changed arbitrarily. For example, in the case where two or more kinds of metals are used as the first electrode material, the metal ratio is adjusted by adjusting the film thickness of the metal thin film or alloying when each metal is laminated. In the case of lamination, the ratio of each metal of the alloy is adjusted.
[0010]
Further, in the present invention, it is preferable that gold (Au) is contained as the fourth electrode material of the electrode in order to obtain the effect. In the fourth electrode material made of Au, when the electrodes are formed together with the first to third electrode materials, the stacking order of the materials is not particularly limited, but preferably the top of the n electrode farthest from the n-type layer. It is formed. Au can prevent the electrode from being oxidized and increase the bonding strength with a ball made of a wire.
[0011]
After the third electrode material is laminated from the first electrode material as described above, or after the fourth electrode material is laminated from the first electrode material, contact between the laminated electrode material and the nitride semiconductor layer is performed. Annealing is performed to improve the ohmic contact. At that time, if the first and second electrode materials use two or more kinds of metals and each metal is laminated as a multilayer film, the multilayer film is multilayered depending on annealing conditions (mainly heat), the film thickness of the electrode material, etc. Part or all of the film is alloyed. In some cases, an alloy is formed between the stacked electrode materials.
The alloying referred to in the present invention is a state in which the metals are not uniformly mixed but rather integrated. Moreover, even when not alloyed, the metal thin film is not clearly separated, and slight metal movement occurs near the contact surface of each electrode material. Alloying as referred to in the present invention may occur at the contact surface.
[0012]
In the present invention, the thickness of the n-electrode is the total film thickness after lamination of each electrode material, and the film thickness of the n-electrode is adjusted by changing the film thickness of each electrode material.
The film thickness of the first electrode material is 10 nm to 200 nm, preferably 10 nm to 50 nm. Within this range, an n-type layer and an ohmic are easily obtained.
The film thickness of the second electrode material is 50 nm to 500 nm, preferably 100 nm to 200 nm. Within this range, an n-type layer and a preferable ohmic can be obtained, and an electrode stable against heat can be obtained.
The film thickness of the third electrode material is 100 nm to 1000 nm, preferably 300 nm to 500 nm. Within this range, the oxidation of the electrode can be prevented, and the adhesive strength is improved.
The film thickness of the fourth electrode material is 100 nm to 1 μm, preferably 200 nm to 500 nm. Within this range, the electrode is satisfactorily prevented from being oxidized, and when the fourth electrode material is used on the top of the n-electrode, the adhesion strength with the ball is improved.
[0013]
In the present invention, the n-electrode is formed by laminating the first to third or fourth electrode materials. The order of lamination of the electrode materials is not particularly limited as described above, and the preferred order of lamination is preferably to form the electrodes by laminating each of the first, second, and third electrode materials. These electrode materials are laminated with a metal or an alloy using an apparatus such as vapor deposition or sputtering to form an electrode.
In the case of the first and second electrode materials using two or more kinds of metals as the electrode material, the multilayer film in which one kind of metal is laminated may be alloyed by annealing treatment.
[0014]
In the present invention, after the first to third electrode materials are laminated or after the first to fourth electrode materials are laminated, an annealing treatment is performed in order to obtain a good ohmic contact. The annealing temperature is 400 ° C. or higher, preferably 600 ° C. or higher, and the upper limit is not particularly limited, but is preferably 1200 ° C. or lower. Annealing at 400 ° C. or higher is preferable because the resistivity starts to decrease and a preferable ohmic contact is obtained, and when it is 1200 ° C. or lower, decomposition of the nitride semiconductor can be prevented.
[0015]
In the present invention, the nitride semiconductor on which the electrode is formed is grown using a vapor phase growth method such as metal organic chemical vapor deposition (MOCVD, MOVPE) or hydride vapor phase epitaxy (HDCVD). The n-electrode is formed on an n-type nitride semiconductor, and the p-electrode is formed on a p-type nitride semiconductor. Here, n-type or p-type refers to a nitride semiconductor containing n-type or p-type impurities. Further, the n-electrode of the present invention can be applied to a nitride semiconductor having any layer structure. The p electrode formed in the p-type layer together with the n electrode of the present invention may be any one.
[0016]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to this.
[Example 1]
Example 1 according to the present invention is a production example of the nitride semiconductor element (LD element) shown in FIG. 4 and is produced by the following procedure.
First, the substrate 10 made of sapphire (C-plane) is set in a reaction vessel, and the inside of the vessel is sufficiently replaced with hydrogen, and then the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate.
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as the carrier gas, ammonia (NH ₃ ) and TMG (trimethylgallium) are used as the source gas, and a buffer layer 11 made of GaN is formed on the substrate 10 to a thickness of about 200 Å. Grow in.
[0017]
After growth of the buffer layer 11, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., similarly, TMG and ammonia gas are used as the source gas, and the second buffer layer 112 made of undoped GaN with a carrier concentration of 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 5 μm. The second buffer layer 112 is _{In X Al Y Ga 1-X} -Y N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) can be configured in its composition but is not intended asks particular, Al preferably undoped Al _Y Ga _1-Y N (Y value) of 0.1 or less, most preferably undoped GaN.
Subsequently, at 1050 ° C., an n-side contact layer 12 made of n-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ is grown to a thickness of 1 μm using TMG, ammonia, and silane gas (SiH ₄ ) as an impurity gas. . The n-side contact layer 12 is more preferably formed of a superlattice.
[0018]
Next, the temperature is set to 800 ° C., TMG, TMI (trimethylindium) as the source gas, ammonia, silane gas as the impurity gas, and In _0.1 Ga _0.9 N doped with Si at 5 × 10 ¹⁸ / cm ^3. An anti-cracking layer 13 is grown to a thickness of 500 angstroms.
[0019]
Then, the temperature is set to 1050 ° C., and TMA (trimethylaluminum), TMG, ammonia, and silane gas are used, and a first n-type Al _0.2 Ga _0.8 N doped with Si of 5 × 10 ¹⁸ / cm ³ is used. The layer is grown to a thickness of 20 Å, and then TMA and silane are stopped, and a second layer of undoped GaN is grown to a thickness of 20 Å. This operation is repeated 100 times to grow an n-side cladding layer 14 made of a superlattice layer having a total film thickness of 0.4 μm.
[0020]
Subsequently, an n-side light guide layer 15 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm.
Next, the active layer 16 is grown using TMG, TMI, ammonia, and silane gas. The active layer 16 is maintained at a temperature of 800 ° C., and a well layer made of In _0.2 Ga _0.8 N doped with Si at 8 × 10 ¹⁸ / cm ³ is first grown to a thickness of 25 Å. Next, a barrier layer made of In _0.01 Ga _0.99 N doped with Si 8 × 10 ¹⁸ / cm ³ is grown to a thickness of 50 Å at the same temperature only by changing the molar ratio of TMI. This operation is repeated twice, and an active layer 16 having a total quantum film structure (MQW) having a total film thickness of 175 angstroms and finally a well layer is grown.
[0021]
Next, the temperature is raised to 1050 ° C., TMG, TMA, ammonia are used as the source gas, Cp ₂ Mg (cyclopentadienylmagnesium) is used as the impurity gas, the band gap energy is larger than that of the active layer, and Mg is 1 × 10 ^A p-side cap layer 17 made of p-type Al _0.3 Ga _0.7 N doped with ²⁰ / cm ³ is grown to a thickness of 300 Å.
Subsequently, at 1050 ° C., a p-side light guide layer 18 made of undoped GaN having a band gap energy smaller than that of the p-side cap layer 17 is grown to a thickness of 0.1 μm.
[0022]
Subsequently, using TMG, TMA, ammonia, and Cp ₂ Mg, a first layer made of p-type Al _0.2 Ga _0.8 N doped with 1 × 10 ²⁰ / cm ³ of Mg at 1050 ° C. was formed to a thickness of 20 Å. The film is grown with a film thickness, and then only TMA is stopped, and a second layer made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown with a film thickness of 20 Å. This operation is repeated 100 times to form a p-side cladding layer 19 made of a superlattice layer having a total film thickness of 0.4 μm.
Finally, the p-side contact layer 20 made of p-type GaN doped with 2 × 10 ²⁰ / cm ^{3 of} Mg is grown on the p-side cladding layer 19 at 1050 ° C. to a thickness of 150 Å.
[0023]
After the completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 1, the uppermost p-side contact layer 20 and the p-side cladding layer 19 are etched by an RIE apparatus to form a ridge shape having a stripe width of 4 μm. To do.
[0024]
Next, a mask is formed on the ridge surface, and as shown in FIG. 1, the surface of the n-side contact layer 12 is exposed so as to be symmetrical with respect to the striped ridge.
[0025]
Next, a p-electrode 21 made of Ni and Au is formed on almost the entire surface of the stripe ridge outermost surface of the p-side contact layer 20. On the other hand, Ti is deposited in a thickness of 10 nm, Al is 200 nm, Rh is 200 nm, and Au is deposited in a thickness of 200 nm to form an n-electrode 23 on almost the entire surface of the striped n-side contact layer 12.
After the p-electrode 14 is formed, the mask is removed, the wafer is put in an annealing apparatus, and annealing is performed at 600 ° C. for 10 minutes in an inert gas atmosphere.
[0026]
Next, as shown in FIG. 1, an insulating film 25 made of SiO ₂ is formed on the surface of the nitride semiconductor layer exposed between the p-electrode 21 and the n-electrode 23, and the p-electrode is interposed through this insulating film 25. A p-pad electrode 22 and an n-pad electrode 24 electrically connected to 21 are formed.
As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to a polishing apparatus, and the sapphire substrate 1 on the side where the nitride semiconductor is not formed is lapped with a diamond abrasive, The thickness is 50 μm. After lapping, the substrate surface is mirror-finished by polishing with 1 μm with a finer abrasive.
[0027]
After polishing the substrate, the polished surface side is scribed and cleaved in a bar shape in a direction perpendicular to the striped electrode to produce a resonator on the cleaved surface. A dielectric multilayer film made of SiO ₂ and TiO ₂ was formed on the resonator surface, and finally a bar was cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed face up (with the substrate and the heat sink facing each other) on the heat sink, and each electrode was wire-bonded to produce an LD element.
When this laser diode was oscillated at room temperature, good ohmic contact was obtained at room temperature with a threshold current density of 2.9 kA / cm ² and a threshold voltage of 4.4 V. Furthermore, when 100 laser diodes were randomly extracted from this LD element and continuously oscillated in a high temperature and high humidity state of 40 ° C. and 90% RH, each element showed a life of 10 hours or more, and the electrode deteriorated even at high humidity. It has been found that it has sufficient durability.
[0028]
[Example 2]
In Example 1, the electrode formed on the surface of the n-type GaN contact layer was formed in the same manner except that Zr was 60 nm, Si was 30 nm, Rh was 200 nm, and Au was deposited in a thickness of 200 nm. A good ohmic contact was obtained. Further, when continuous oscillation was performed in a high-temperature and high-humidity state as in Example 1, good results were obtained as in Example 1.
[0029]
[Example 3]
In Example 1, the electrode formed on the surface of the n-type GaN contact layer was formed in the same manner except that Ti was deposited in order of 40 nm, Al 150 nm, Ti 30 nm, Rh 200 nm, and Au 200 nm. As a result, similarly good ohmic contact was obtained. Further, when continuous oscillation was performed in a high-temperature and high-humidity state in the same manner as in Example 1, almost the same result as in Example 1 was obtained.
[0030]
[Comparative Example 1]
In Example 1, the electrode formed on the surface of the n-type GaN contact layer was formed in the same manner except that Ti was deposited in a thickness of 10 nm, Si was deposited in a thickness of 50 nm, and Au was deposited in a thickness of 200 nm. When contact was obtained, continuous oscillation was performed in a high-temperature and high-humidity state in the same manner as in Example 1. As a result, continuous oscillation was possible only for less than 1 hour.
[0031]
【The invention's effect】
INDUSTRIAL APPLICABILITY The present invention can provide an n-electrode that has a very preferable ohmic contact with an n-type nitride semiconductor layer and that does not easily deteriorate even when a light-emitting element is used under severe conditions and that has a good lifetime characteristic of the element. .
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor light emitting device as an embodiment capable of providing an n-electrode according to the present invention.
[Explanation of symbols]
10 .... substrate 11 ... buffer layer 112 ... second buffer layer 12 ... n-side contact layer 13 ... crack prevention layer 14 ... n-side cladding layer ( Superlattice layer)
15 ... n-side light guide layer 16 ... active layer 17 ... cap layer 18 ... p-side light guide layer 19 ... p-side cladding layer (superlattice layer)
20... P-side contact layer 21... P electrode 22... P pad electrode 23... N electrode 24.

Claims (3)

A method of manufacturing a nitride semiconductor light emitting device having a p-type nitride semiconductor at least n-type nitride gallium nitride-based semiconductor and gallium nitride, on the n-type nitride semiconductor surface, titanium, zirconium and tungsten A first electrode material composed of at least one of the following, a second electrode material composed of at least one of aluminum, silicon and germanium, and a third electrode material composed of rhodium, the first electrode material or the second electrode material A step of laminating the first electrode material and the second electrode material as a multilayer film, and laminating the third electrode material thereon to form an electrode material. When,
A method of manufacturing a nitride semiconductor light emitting device, comprising: after the step of forming the electrode material, alloying a part or all of the multilayer film by annealing the electrode material.   The method for manufacturing a nitride semiconductor light-emitting element according to claim 1, wherein, in the step of forming the electrode material, a fourth electrode material made of gold is formed on the third electrode material.   In the step of forming the electrode material, the first electrode material is laminated in contact with the n-type nitride semiconductor, and the second electrode material and the third electrode material are sequentially laminated thereon. Item 3. The method for producing a nitride semiconductor light emitting device according to Item 1 or 2.

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